Description

A fun thought experiment I heard of. Makes you think about nothing. ;)
Ok, it was an ice skater, I think, but it's not essential. I took a Ballerina here...
There is an answer, it seems simple but is quite interesting.

Music:

"Illusions Déçues" by Whiteyes
http://www.jamendo.com/en/track/37338
is licensed under a Creative Commons license:
http://creativecommons.org/licenses/by-nc-nd/3.0/